:at start up, then if all wiring connections are good the alt should work immediately. As a check start the car cold and check the voltage across the + and - battery posts it should be about 14+ volts. If not I would suspect the alt is a bad unit and has faulty diodes, especially since you just replaced it. If it reads OK but later stops working and the belt squeals like lock up the alt is faulty and the diodes are bad, happened to me. :What were the symptoms of the alternator that caused you to replace it? :Is the replaced alt a new OEM unit or a parts store rebuilt or a re-manufactured unit? Remans are better than rebuilt units. :When you tension the belts DONOT over tighten them beyond factory settings. Excessive tightening will be bad for the bearings and cause premature unit failure. If tightened correctly and they still squeal the belts need to be replaced with new units. Spraying with chemicals is a temp measure.
Alternator is a reman unit, also belt is new. Had my battery checked, it tested bad. Going to get a new one tomorrow. To see if that helps out at all.